1. Field of the Invention:
The present invention relates to a hollow fiber membrane type artificial lung of an externally blood-flowing type in which blood flows outside, a hollow fiber membrane and oxygen is introduced into a space of the hollow fibers membrane and a fiber arrangement method therefor. More particularly, the present invention relates to a hollow fiber membrane type artificial lung revealing a reduced pressure loss, capable of preventing blood channeling (a phenomenon of a nonuniform blood flow while being deviated locally), exhibiting an excellent gas exchanging efficiency and significantly reduced size and displaying an advantage in that a necessary quantity of blood to be enclosed can be reduced.
2. Description of the Related Art:
An artificial lung has been used to perform blood gas exchange at the time of a heart opening operation. Artificial lungs are exemplified by a bubble type artificial lung and a membrane type artificial lung. The bubble type artificial lung is arranged to introduce a gas into blood, and blood and the gas are thereby directly brought into contact with each other. In consequence, a problem arises in that blood corpuscles will be broken, that is, hemolysis takes place. On the other hand, the membrane type artificial lung is arranged to perform the blood gas exchange via a gas permeable membrane. Therefore, it is widely clinically used since the membrane type artificial lung is a rather physiological method in comparison to the bubble type artificial lung.
The membrane type artificial lung uses a gas permeable hollow fiber membrane for most part, the membrane type artificial lung being exemplified by an internal flow system in which blood flows in a space in the hollow fiber membrane and an external flow system in which the same flows outside the hollow fiber membrane. The internal flow system is arranged in such a manner that blood flows in a space in the hollow fiber membrane the fiber having an extremely small diameter of several tens to several hundred of .mu.s. Therefore, an excessively large pressure loss takes place when blood circulates, causing the blood corpuscles to be damaged. Namely, the hemolysis will take place. What is even worse, blood flowing in the portions except for the portion near the surface of the membrane cannot easily be oxidized since blood flows in the form of a laminar flow. Therefore, an excessively large membrane area must be given in order to improve the gas exchanging performance. In consequence, the quantity of blood to be charged, that is, the quantity of blood to be circulated outside the body is enlarged excessively.
When a centrifugal pump or a pulsation flow pump which has been used recently is used to perform the body outside circulation, the pressure loss in the artificial lung must be reduced as much as possible. Therefore, it is preferable to employ the external flow system.
In the external flow system, blood flows outside the hollow fiber membrane. As a result, the problems experienced with the above-described internal flow system can be overcome. However, another problem arises in that the blood flow will deviate to a passage having relatively small resistance (a so-called channeling takes place). In consequence, the gas exchanging performance of the artificial lung will excessively deteriorate. Accordingly, a structure in which the hollow fibers are twilled or another structure in which the hollow fibers are woven have been developed in order to prevent the drift of the blood flow. In addition, although a structure in which the hollow fibers are arranged linearly has been developed, an excessively precise task must be performed to uniformly arrange the hollow fibers. In the structure in which the hollow fibers are twilled or the structure in which the same are woven, the blood flow becomes too complicated. In consequence, an excessively large resistance is generated when blood flows, and the pressure loss becomes excessively large. In the structure in which the hollow fibers are arranged linearly, the same cannot satisfactorily equally be arranged. Therefore, the membrane area must be enlarged in order to improve the gas exchanging performance. If the membrane area is enlarged for the purpose of overcoming the abovedescribed problem, the necessary quantity of blood to be filled in the artificial lung is enlarged. In consequence, a problem arises in that the body outside circulation operation cannot be easily performed without a blood transfusion.
The above-described problems are considerably influenced by a state where the hollow fibers is arranged in a bundle, the packing ratio, the positions of the blood inlet and outlet ports and the blood passage. Accordingly, there have been a method for improving the gas exchanging efficiency and the pressure loss by enlarging the area of the membrane or enlarging the area of the fluid passage and another method capable of reducing the pressure loss by allowing blood to flow in the side portion of the hollow fiber bundle. However, the former method encounters a problem in that a large quantity of blood must be enclosed although the pressure loss can be prevented. Another problem arises in the latter method in that it cannot easily be combined with a pulsation pump or the like although the pressure loss can be further prevented in comparison to the pressure loss taken place in the internal flow system.
Another structure has been disclosed which is arranged in such a manner that the hollow fiber membrane is wound around a cylindrical member to form a bundle so as to prevent the blood drift and to obtain an excellent gas exchanging performance. However, that structure generates an excessively large pressure loss since blood, which has been supplied from the blood port through a blood inlet (a portion through which blood is introduced into the hollow fiber bundle), is rapidly introduced into the hollow fiber bundle and, what is even worse, the flow passage is rapidly narrowed. If the blood inlet is enlarged in order to prevent that problem, the overall size of the artificial lung is excessively enlarged.